From a purely functional point of view the more efficiently a machine performs its task of processing material then the better it is. But, in order for a machine to be viable it must also be safe. Safety therefore must be regarded as a crucial component of machine design and considered early in the overall machine design process.

Prevailing global safety system design standards such as ISO13849-1/2, ANSI B11 and ANSIZ244.1 readily refer to risk assessment as the foundation from which all safety related design decisions should flow. Moreover, their normative references to Risk Assessment and Risk Reduction standards (ex: ANSI B11.0, ISO12100) point to a methodology that provides a well-defined approach to achieving safety goals.

This Machine Safety Lifecycle, as shown above, consists of five steps the underpinnings of which are:

Risk Assessment based on a clear understanding of the machine limits and functions and the tasks that may be required to be performed at the machine throughout its life

Risk Reduction is performed, if necessary and safety measure are selected based on the information derived from the risk assessment.

As a design strategy the machine safety life cycle process will help ensure that proper and compliant safety practices have been implemented. It is a repeatable process that helps remove uncertainty and eliminate omissions and errors in design.

The steps of the life cycle include:

Risk Assessment: Identifies hazards and estimates associated risk. Key considerations in risk assessment include severity of an injury from the hazard, frequency of exposure to the hazard and ability to avoid the hazard if exposed to it. The result of the risk assessment will be a measure (PLr, Cat, Risk Reduction) that will need to be met in design

Functional Requirements: Evaluates safe guarding options based on industry acceptable solutions and selected mitigation techniques. In this step a detailed description is developed defining how the machine will function in all modes of operation. Key considerations include; all modes of operation, safe state, triggering event, reaction, reset conditions and circuit performance.

Installation and Validation: Verifies that safety system is operating within specified parameters and applicable standards have been met. Validation typically involves implementing (non-destructive) faults to the safety system to ensure that the safety function reacts as planned.

Maintain and Improve: Verifies that system requirements operate within specified parameters throughout the life of the equipment. Key considerations include schedule of safety system maintenance, periodic testing of safety function and re-evaluation process for safety function modifications and upgrades

While the purpose of the production control system is to produce and the safety system is to protect, they are not mutually exclusive and should not be held apart during design. In fact, significant gains in OEE can be achieved by including safety early in the overall design process…

Shared diagnostics on common HMI for faster troubleshooting and fault recovery

Safety System that is coordinated with machine operating modes (auto, manual, set up, cleaning, etc.

Zone control enabling continuing production flow in areas not effected by shut down

Coordinated/faster recovery of production systems after a safety event

So, achieving a Safe and Productive Workplace starts by leveraging the machine safety lifecycle early in the machine design process and following the five steps described above.

Interested in learning more? Here are some new links and educational documents you might find helpful: